1. Field of the Invention
The present invention relates to an optical pointing system and, more specifically, to an optical pointing system capable of adaptively changing a maximum search window and/or a sampling rate according to a quantity of incident light and a movement speed and a method for calculating a movement value thereof.
2. Description of the Related Art
FIG. 1 shows a general optical pointing system comprising a light source 8, a lens 5, and an image sensor of a sensor circuit 3 (not shown).
In FIG. 1, Reference numeral 2 represents a worktable surface, and 4, 6 and 7 represent light.
In the optical pointing system shown in FIG. 1, the light 7 emitting from the light source 8 is reflected from the worktable surface 2, and the reflected light 6 passes through the lens 5. And then, the light 4 passing through the lens 5 is input to the image sensor 3 composed of a CMOS (Complementary Metal Oxide Semiconductor) device.
An image of the worktable is successively detected by means of the image sensor 3 and is stored in a memory (not shown) of the sensor circuit as image data. The sensor circuit calculates a correlation value between the image data currently inputted to the memory and the image data previously stored in the memory, calculates the movement value, and transmits it to a system such as a computer.
FIG. 2 shows a block diagram of a sensor circuit of a conventional optical pointing system, comprising an image sensor 210, an A/D converter 220, a shutter control circuit 230, a movement value calculation circuit 240, and a PC interface circuit 250.
A function of each block shown in FIG. 2 is described as follows.
The image sensor 210 receives light reflected from a workable surface through the lens under the control of a shutter control signal SHCO to detect image data. The A/D converter 220 receives an analog signal outputted from the image sensor 210 to convert the analog signal to a digital signal. The shutter control circuit 230 generates the shutter control signal SHCO for controlling an electronic shutter (not shown) in the image sensor 210 such that an output of the AND converter 220 has a uniform distribution using the image data, which is an output signal of the A/D converter 220. The electronic shutter not shown comprises a CMOS device in the sensor circuit. The movement value calculation circuit 240 calculates and outputs the movement value of the image data, which is the output signal of the A/D converter 220, at a fixed sampling rate using a fixed maximum search window and mask window. The PC interface circuit 250 transmits the movement value outputted from the movement value calculation circuit 240 to a computer (not shown) at a fixed report rate. In other words, the PC interface circuit 250 stores the movement value outputted from the movement value calculation circuit 240, and then transmits the movement value at the fixed report rate required in the computer (not shown).
The sensor circuit of the conventional optical pointing system as described above always calculated a correlation value between image frame data previously inputted to the memory and newly inputted image frame data at the fixed sampling rate to output the movement value. For example, all the circuits in the sensor circuit were operated at the sampling rate fixed with 1500 or 2000 times per second as a reference one. Further, the sensor circuit of the conventional optical pointing system found the movement value and transmitted the result to the computer at the fixed report rate.
Moreover, the conventional optical pointing system could change a quantity of incident light only within a shutter exposure time, which has a predetermined operation time of the electronic shutter adjusting the quantity of incident light inputted to the image sensor 210, and the movement value calculation circuit 240 also calculated the correlation value at the predetermined sampling rate using the fixed maximum search window.
Meanwhile, when the sampling rate, the shutter exposure time, and the maximum search window are predetermined, if the quantity of light is extremely reduced, the optical pointing system is operated such a state that the quantity of light is increased by extending the exposure time of the electronic shutter in order to suffice the quantity of incident light. However, although the maximum time of a shutter exposure period adapted to the predetermined sampling rate is reached, when the required quantity of light is not inputted, the image sensor cannot represent a workable surface pattern as it is. As such, when the quantity of light is insufficient, the optical pointing system cannot discriminate a value of the workable surface pattern, so that the movement value cannot be found.